Electronic components are typically encapsulated by transfer molding. For rapid and easy release from mold cavities, mold release agents are included in the formulation of transfer molding compounds. After the molding process, these release agents are present on the surface of the molded components. It is very challenging for thermal interface materials (TIMs) to adhere to the resulting very low surface energy surfaces (<35 ergs/cm2). In the past, the surface of the component has been treated to provide higher energy surfaces for improved TIM adhesion. Such treatments include wiping the surface with isopropyl alcohol, abrading the surface and then wiping with isopropyl alcohol, or exposing the surface to a plasma cleaning process or ultraviolet (UV) light and/or ozone. These are non-routine processes that are typically performed at the card assembly factory and are significantly manual in nature.
Heat dissipation has become a major technical challenge for complex printed circuit board (PCB) assemblies. Rather than using individual heat sinks for every component, very large (in excess of four square feet or 0.37 square meters), common heat spreaders are being used over an array of components and component types. Due to the mismatch in coefficient of thermal expansion between the heat spreader, which is typically aluminum (coefficient of thermal expansion 23.6 ppm/C (parts per million per degree Celsius)) and PCB assembly (coefficient of thermal expansion ˜17 ppm/C) and the large thermal mass of both the heat spreader and PCB assembly, significant relative movement occurs during temperature excursions resulting from powering the circuitry on and off. The TIM which physically bridges the gap between the heat spreader and PCB must accommodate this movement without breaking down. Because of the inherent low surface energy of transfer molded component surfaces, the TIM can slide along these surfaces when it is sheared or compressed by the relative movement, and over time, can move out of the gap. The result is increasing thermal resistance which leads to decreased reliability, and in a worst case scenario, fire. Because of the size of the PCB assemblies, batch processing in plasma or UV and/or ozone is very costly. Abrasion and isopropyl wipe techniques are undesirable as well because of the handling and debris generation.